1. Field of Invention
The present invention relates to a serial printing device which has a type drum carrying a plurality of character-bearing elements movable radially outwardly thereto and axially rotatable to bring a selected character-bearing element thereon to a printing position and wherein the selected character-bearing element is moved towards a platen to effect printing impact.
2. Description of the Prior Art
It is known to achieve this by leaving the drum bodily unmoved and by striking the selected element with a hammer to project this element radially from the drum, the elements being biased radially inwardly. A disadvantage of this is that the stroke which can be imparted to the element by the hammer is limited and the drum must therefore be near the platen. This obscures the just-printed characters unduly.
It is also known to move the drum bodily towards the platen but it is then necessary to make the selected character-bearing element protrude, otherwise the adjacent characters tend to print partially. To this end, a cam pushes each element out as it moves to the printing point. This has the disadvantage that the elements are constantly pushed out as the drum rotates, leading to excessive wear and fatigue of the resilient means which bias the elements back into the drum.